org.xml.sax.helpers
Class NamespaceSupport

Encapsulate Namespace logic for use by applications using SAX,
or internally by SAX drivers.

This module, both source code and documentation, is in the
Public Domain, and comes with NO WARRANTY.
See http://www.saxproject.org
for further information.

This class encapsulates the logic of Namespace processing: it
tracks the declarations currently in force for each context and
automatically processes qualified XML names into their Namespace
parts; it can also be used in reverse for generating XML qnames
from Namespaces.

Namespace support objects are reusable, but the reset method
must be invoked between each session.

Note that this class is optimized for the use case where most
elements do not contain Namespace declarations: if the same
prefix/URI mapping is repeated for each context (for example), this
class will be somewhat less efficient.

Although SAX drivers (parsers) may choose to use this class to
implement namespace handling, they are not required to do so.
Applications must track namespace information themselves if they
want to use namespace information.

NSDECL

The namespace declaration URI as a constant.
The value is http://www.w3.org/xmlns/2000/, as defined
in a backwards-incompatible erratum to the "Namespaces in XML"
recommendation. Because that erratum postdated SAX2, SAX2 defaults
to the original recommendation, and does not normally use this URI.

This is the Namespace URI that is optionally applied to
xmlns and xmlns:* attributes, which are used to
declare namespaces.

NamespaceSupport

public NamespaceSupport()

Create a new Namespace support object.

Method Detail

reset

public void reset()

Reset this Namespace support object for reuse.

It is necessary to invoke this method before reusing the
Namespace support object for a new session. If namespace
declaration URIs are to be supported, that flag must also
be set to a non-default value.

pushContext

Start a new Namespace context.
The new context will automatically inherit
the declarations of its parent context, but it will also keep
track of which declarations were made within this context.

Event callback code should start a new context once per element.
This means being ready to call this in either of two places.
For elements that don't include namespace declarations, the
ContentHandler.startElement() callback is the right place.
For elements with such a declaration, it'd done in the first
ContentHandler.startPrefixMapping() callback.
A boolean flag can be used to
track whether a context has been started yet. When either of
those methods is called, it checks the flag to see if a new context
needs to be started. If so, it starts the context and sets the
flag. After ContentHandler.startElement()
does that, it always clears the flag.

Normally, SAX drivers would push a new context at the beginning
of each XML element. Then they perform a first pass over the
attributes to process all namespace declarations, making
ContentHandler.startPrefixMapping() callbacks.
Then a second pass is made, to determine the namespace-qualified
names for all attributes and for the element name.
Finally all the information for the
ContentHandler.startElement() callback is available,
so it can then be made.

The Namespace support object always starts with a base context
already in force: in this context, only the "xml" prefix is
declared.

declarePrefix

Declare a Namespace prefix. All prefixes must be declared
before they are referenced. For example, a SAX driver (parser)
would scan an element's attributes
in two passes: first for namespace declarations,
then a second pass using processName() to
interpret prefixes against (potentially redefined) prefixes.

This method declares a prefix in the current Namespace
context; the prefix will remain in force until this context
is popped, unless it is shadowed in a descendant context.

To declare the default element Namespace, use the empty string as
the prefix.

Note that there is an asymmetry in this library: getPrefix will not return the "" prefix,
even if you have declared a default element namespace.
To check for a default namespace,
you have to look it up explicitly using getURI.
This asymmetry exists to make it easier to look up prefixes
for attribute names, where the default prefix is not allowed.

Parameters:

prefix - The prefix to declare, or the empty string to
indicate the default element namespace. This may never have
the value "xml" or "xmlns".

processName

Process a raw XML qualified name, after all declarations in the
current context have been handled by declarePrefix().

This method processes a raw XML qualified name in the
current context by removing the prefix and looking it up among
the prefixes currently declared. The return value will be the
array supplied by the caller, filled in as follows:

parts[0]

The Namespace URI, or an empty string if none is
in use.

parts[1]

The local name (without prefix).

parts[2]

The original raw name.

All of the strings in the array will be internalized. If
the raw name has a prefix that has not been declared, then
the return value will be null.

Note that attribute names are processed differently than
element names: an unprefixed element name will receive the
default Namespace (if any), while an unprefixed attribute name
will not.

Parameters:

qName - The XML qualified name to be processed.

parts - An array supplied by the caller, capable of
holding at least three members.

isAttribute - A flag indicating whether this is an
attribute name (true) or an element name (false).

Returns:

The supplied array holding three internalized strings
representing the Namespace URI (or empty string), the
local name, and the XML qualified name; or null if there
is an undeclared prefix.

getPrefixes

Return an enumeration of all prefixes for a given URI whose
declarations are active in the current context.
This includes declarations from parent contexts that have
not been overridden.

This method returns prefixes mapped to a specific Namespace
URI. The xml: prefix will be included. If you want only one
prefix that's mapped to the Namespace URI, and you don't care
which one you get, use the getPrefix
method instead.

Note: the empty (default) prefix is never included
in this enumeration; to check for the presence of a default
Namespace, use the getURI method with an
argument of "".

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